The clathrin coated vesicle cycle drives synaptic vesicle recycling and is essential for the maintenance of repeated rounds of neurotransmission. Many of the structural components of the clathrin endocytic machinery have been identified, but our understanding of the molecular mechanisms underlying and regulating clathrin-mediated endocytosis is still in its infancy. Moreover, only one enzyme, the GTPase dynamin, has been identified to play a role in clathrin-mediated endocytosis even though these reactions are ATP-dependent. My laboratory has pioneered the development of a set of cell-free assays that together, faithfully and efficiently reconstitute each step in the clathrin-coated vesicle cycle, including coated pit assembly, coated vesicle formation and the sequential uncoating reactions that recycle the coat proteins, freeing the enclosed vesicles. Using these well-characterized assays, we are in a unique position to elucidate the molecular mechanisms that govern synaptic vesicle recycling. The long-term goal of this proposal is to identify the minimal set of cytosolic and peripheral membrane proteins required to reconstitute clathrin-mediated endocytosis and to complete the clathrin-coated vesicle cycle. To meet this objective, we propose the following Specific Aims: 1) To develop a novel assay for coated vesicle budding from highly enriched plasma membranes to enable identification of peripheral and integral membrane components of the endocytic machinery;2) To determine the hierarchy of events leading to coated pit assembly and endocytic clathrin coated vesicle formation;3) To identify minimal cytosolic components required for endocytic coated vesicle formation;4) To identify proteins that regulate the uncoating reaction and to test the role of hsc70, the uncoating ATPase in vivo;and, 5) To develop transient expression systems in primary neurons to demonstrate that protein interactions and mechanisms identified in vitro are required for synaptic vesicle recycling in vivo.